Ginsenoside Rg3 enhances large conductance Ca2+-activated potassium channel currents: a role of Tyr360 residue.

Ginsenosides, active ingredients of Panax ginseng, are known to exhibit neuroprotective effects. Large-conductance Ca(2+)-activated K(+) (BK(Ca)) channels are key modulators of cellular excitability of neurons and vascular smooth muscle cells. In the present study, we examined the effects of ginsenosides on rat brain BK(Ca) (rSlo) channel activity heterologously expressed in Xenopus oocytes to elucidate the molecular mechanisms how ginsenoside regulates the BK(Ca) channel activity. Ginsenoside Rg(3) (Rg(3)) enhanced outward BK(Ca) channel currents. The Rg(3)-enhancement of outward BK(Ca) channel currents was concentration-dependent, voltage-dependent, and reversible. The EC(50) was 15.1 ± 3.1 μM. Rg(3) actions were not desensitized by repeated treatment. Tetraetylammonium (TEA), a K(+) channel blocker, inhibited BK(Ca) channel currents. We examined whether extracellular TEA treatment could alter the Rg(3) action and vice versa. TEA caused a rightward shift of the Rg(3) concentration-response curve (i.e., much higher concentration of Rg(3) is required for the activation of BK(Ca) channel compared to the absence of TEA), while Rg(3) caused a rightward shift of the TEA concentration-response curve in wild-type channels. Mutation of the extracellular TEA binding site Y360 to Y360I caused a rightward shift of the TEA concentration-response curve and almost abolished both the Rg(3) action and Rg(3)-induced rightward shift of TEA concentration-response curve. These results indicate that Tyr360 residue of BK(Ca) channel plays an important role in the Rg(3)-enhancement of BK(Ca) channel currents.